Often minefields are first detected by a mine detonation, resulting in casualties and equipment damage. This method of detection is unacceptable. Thus, when operating in potentially mined areas, expensive and time consuming precautions are undertaken.
Once a minefield is identified, a variety of methods are used to locate individual mines therein. These range from the use of ground penetrating radar to manual detection by visual observation or probing with a pole. A disadvantage of conventional methods is the need to operate close to the mines, often within the minefield itself. This endangers personnel and equipment because of the potential to accidentally trigger a mine.
A preferred embodiment of the present invention provides a new method of recognizing patterns that lead to locating minefields and even detecting individual mines, in particular those designed to be detonated by the passing of vehicles. It makes use of some of the unusual properties of the reflections of electromagnetic waves traveling along the earth's surface, i.e., surface waves, and collectively reflecting off of the arrays of landmines in such minefields. In particular, it exploits the reflections from patterns of symmetric arrays of mines.
While there are different schemes by which landmines are spatially deployed in minefields, the periodic planar array is common. The planar array has the landmines at the intersections of a rectangular grid consisting of rows and columns of mines. In other configurations, the landmines are deployed so that on alternate rows (or columns) they are displaced laterally. These geometries and interactions are analogous to two-dimensional projections of crystal structures that have been shown to respond predictably when X-rayed.
Since these minefields are analogous to crystalline arrays they may be recognized as such when illuminated at appropriate radio frequency (RF) frequencies such as in the HF band. Much theory and applications have been developed on electromagnetic wave interactions with arrays of the above nature. A new journal, Subsurface Sensing Technologies and Applications, is devoted to the overall subject and many other references are available. Although the dimensions and frequencies discussed in this journal and related references vary greatly from a surface wave radar application of a preferred embodiment of the present invention, the discussion of the relationship of wavelength to dimension is equivalent. The theory of operation has been discussed in a paper entitled, “Remote Subsurface Minefield Detection and Recognition from Spectral Signatures,” presented on Nov. 3, 1999.